In recent years, a capsule endoscope that is a swallowable endoscope including an imaging function and a radio communication function has appeared, and a capsule endoscope system that acquires image data on intra-subject images picked up by the capsule endoscope has been developed. In the capsule endoscope system, the capsule endoscope functions to move in the interior of the subject, i.e., interiors of organs such as the stomach and the small intestine according to their peristaltic movements since being swallowed from a subject's mouth for observation (examination) until being naturally discharged from the interior of the subject, and to pick up the intra-subject images at predetermined intervals of, for example, at intervals of 0.5 second.
During movement of the capsule endoscope in the interior of the subject, image data on the images picked up by the capsule endoscope is sequentially transmitted to the outside by radio communication and received by a receiving apparatus through a receiving antenna provided outside of the capsule endoscope. The receiving apparatus can reconstruct the image data based on radio signals sequentially received through the receiving antenna and thereby acquire intra-subject image data by the capsule endoscope. The receiving apparatus sequentially stores the acquired image data in a memory. By carrying the receiving apparatus including a radio communication function and a memory function, the subject can act freely since swallowing the capsule endoscope until the capsule endoscope is naturally discharged. An examiner such as a doctor or a nurse then loads the image data stored in the memory of the receiving apparatus into an image display apparatus, and displays the intra-subject images based on the obtained image data, for example, images of an organ on a display. The examiner can diagnose the subject while observing the images of the organ or the like displayed on the display.
Generally, such an image display apparatus includes a processing function for sequentially displaying a series of images picked up by the capsule endoscope according to time series. For example, if an image of a to-be-observed region in the body of the subject is displayed, the examiner performs an operation for playing the image at slow rate so as to carefully observe the image. Furthermore, if an image of a region other than the to-be-observed image is displayed, the examiner performs an operation for playing the image at fast rate so as to shorten time for observing the series of intra-subject images. In relation to such a technique, there is known an image display apparatus that measures image similarity among sequentially displayed frames, that displays or cuts each image with high similarity at fast display frame rate by accelerating display frame rate if the obtained similarity is high, and that displays each image with low similarity at slow display frame rate by decelerating the display frame rate if the obtained similarity is low (see Patent Document 1).
Patent Document 1: U.S. Pat. No. 6,709,387